1  

Muscular  Tissue  

BIOL  121:  A&P  I  

Chapter  10  

Rob  Swatski  Associate  Professor  of  Biology  

HACC  –  York  Campus  

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2  

Myology  

MoHlity  

ContracHon  

RelaxaHon  

Chemical  energy  à  Mechanical  

energy  

3  

Muscle  Tissue  

Skeletal  muscle  

Cardiac  muscle  

Smooth  muscle  

4  

Skeletal  Muscle  A4ached  to  bone,  skin,  

fascia  

Striated  &  voluntary  

Parallel  fibers  

5  

Cardiac  Muscle  

Heart  muscle  

Striated,  involuntary,  autorhythmic  

Branching  fibers  

6  

Smooth  Muscle  

In  walls  of  viscera  

Nonstriated  &  involuntary  

Tapered  individual  

cells  

7  

FuncHons  of  Muscle  Tissue  

Movement   Stability  Storing  and  TransporHng  Substances  

Thermogenesis  

8  

ProperHes  of  Muscle  Tissue  

Excitability   Extensibility   ContracHlity   ElasHcity  

9  

Skeletal  Muscle  Whole  muscle  

=  organ  

MulQnucleated  muscle  cell  =  

fiber  

Fascicle  

Muscle  belly  à  Tendon  à  

Bone  

10  

ConnecHve  Tissue  

Components  of  Muscle  

Epimysium  

Perimysium  

Endomysium  

Perimysium around fascicle

Satellite cell

Mitochondrion

Endomysium

Myofibril

Muscle fiber

Sarcolemma

Sarcoplasm

Nucleus

OrganizaHon  of  a  fascicle  

12  

Tendons  

Extensions  of  CT    

A4ach  muscle  to  bone  or  to  other  muscle  

Dense  regular  CT  

Aponeurosis  

13  

Nerve  &  Blood  Supply  of  Muscle  

Nerve,  artery,  1-­‐2  veins  per  muscle  

Motor  neuron  supplies  several  

fibers  

Neuromuscular  juncHon  (NMJ)  

14  

15  

Structure  of  Muscle  Fibers  

Sarcolemma  

Transverse  (T)  tubules  

Sarcoplasm:  glycogen  &  myoglobin  

Mitochondria  

Sarcoplasmic reticulum

Sarcolemma

Myofibril

Sarcoplasm

Nucleus

Thick filament Thin

filament

Z disc

Details  of  a  muscle  fiber  

Triad:

Transverse tubule

Terminal cisterns

Mitochondrion

Sarcomere

17  

Myofibrils  

Create  striaHons  

Surrounded  by  sarcoplasmic  reHculum  (SR)  

Thick  &  thin  contracHle  filaments  

18  

19  

Sarcomeres  

Organized  contracQle  units  

Separated  by  z-­‐discs  

Thick  &  thin  filaments  overlap  

20  

21  

Sarcomere  Structure  

M-­‐line  

H-­‐zone  

A-­‐band  

I-­‐band  

Z-­‐disc  

22  

23  

24  

25  

Myofibril  Proteins  ContracHle  proteins  

Regulatory  proteins  

Structural  proteins  

26  

ContracHle  Proteins  

AcHn  

Myosin  

Myosin-binding site (covered by tropomyosin)

PorHon  of  a  thin  filament  

Actin Troponin Tropomyosin

28  

29  

30  

31  

Regulatory  Proteins  

Troponin  

Tropomyosin  

32  

Structural  Proteins  

Nebulin:  alignment  

TiHn:  extensibility  &  elasQcity  

Myomesin:  anchorage  

Dystrophin:  transmits  tension  

33  

Sarcolemma Sarcoplasmic reticulum (SR)

Transverse tubule

Terminal cistern of SR

Sarcoplasm

Membrane protein

Nucleus Z

disc

Dystrophin

Thin filament Thick filament

Sarcomere

SimplisHc  representaHon  of  a  muscle  fiber  

Myofibril

= Ca2+

Key:

= Ca2+ release channels

= Ca2+ active transport pumps

Glycogen granules Myoglobin Mitochondrion

Z disc

35  

Sliding  Filament  Mechanism  of  ContracHon    

36  

NMJ  

Axon  terminal  of  motor  neuron  

SynapHc  end  bulb  

Motor  end  plate  

Synapse  

SynapHc  cleW  

Neuromuscular  juncHon  

Axon collateral of somatic motor neuron

Axon terminal

Synaptic end bulb

Neuromuscular junction (NMJ)

Sarcolemma

Myofibril in muscle fiber

Muscle fiber

38  

Muscle  ContracHon  

Nerve  impulse  reaches  axon  

terminal  at  NMJ  

SynapHc  vesicles  à  ACh  into  cle\  

ACh  à  receptors  on  sarcolemma  

(motor  end  plate)  

Na+  channels  OPEN  

Na+  “soaks”  into  muscle  fiber  

Enlarged  view  of  the  neuromuscular  juncHon  

Axon terminal

Nerve impulse

Synaptic vesicle containing acetylcholine (ACh)

SYNAPTIC END BULB Synaptic cleft (space)

Ca2+ Voltage-gated Ca2+ channel

Sarcolemma

MOTOR END PLATE

Binding  of  acetylcholine  to  ACh  receptors  in  the  motor  end  plate  

ACh is released from synaptic vesicle

Synaptic cleft (space)

ACh binds to ACh receptor

Junctional fold

Synaptic end bulb

ACh is broken down

MOTOR END PLATE

Muscle action potential is produced

Na+

Ca2+

1

2

4

3

Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh).

1

ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP).

Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron.

ACh receptor

Synaptic vesicle filled with ACh

Muscle action potential

Transverse tubule

Muscle AP traveling along transverse tubule opens Ca2+

release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm.

SR Ca2+

Ca2+ binds to troponin on the thin filament, exposing the binding sites for myosin.

Elevated Ca2+

Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.

Muscle relaxes.

Troponin–tropomyosin complex slides back into position where it blocks the myosin binding sites on actin.

Ca2+ active transport pumps

Ca2+ release channels in SR close and Ca2+

active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm.

Ca2+

Nerve impulse

2

3

4

5

6 7

8

9

42  

Muscle  ContracHon  

Muscle  acHon  potenHal  à  

sarcolemma  &  T-­‐tubules  

SR  à  Ca+2  into  sarcoplasm  

Ca+2  binds  to  troponin  

43  

Muscle  ContracHon  

Tropomyosin  swivels  open  

Exposes  myosin-­‐binding  sites  (on  

acQn)  

ContracHon  Cycle  begins  

44  

ContracHon  Cycle  

1.  ATP  hydrolysis  at  myosin  head  

2.  Binding  of  myosin  heads  to  

acHn  (crossbridges)  

3.  ContracHon  =  power  stroke  

4.  Detachment  of  myosin  heads  

45  

1.  ATP  hydrolysis    

46  

2.  Binding  of  myosin  heads  to  acHn  

47  

3.  ContracHon  =  power  stroke  

48  

4.  Detachment  of  myosin  heads  

Myosin heads hydrolyze ATP and become reoriented and energized

Myosin heads bind to actin, forming cross-bridges

As myosin heads bind ATP, the cross-bridges detach from actin Myosin cross-bridges

rotate toward center of sarcomere (power stroke)

ADP

ADP

ADP

P

P

ATP

ATP

Key: = Ca2+

Contraction cycle continues if ATP is available and Ca2+ level in sarcoplasm is high

1

2

3 4

50  

51  

ContracHon  

52  

RelaxaHon  

53  

Length-­‐Tension  

RelaHonship  

Tension  =  force  of  contracQon  

OpQmal  sarcomere  length  

Overstretched  

Understretched  

54  

Muscle  Metabolism  

CreaHne  phosphate  

Anaerobic  glycolysis  

Aerobic  cellular  respiraHon  

55  

CreaHne  Phosphate  

Made  from  excess  ATP  in  resQng  muscle  

15  sec  =  maximum  contracQon  

Short,  intense  bursts  of  energy  

56  

Anaerobic  Glycolysis  

Makes  ATP  from  glucose  

breakdown  during  glycolysis  

If  no  O2:  Pyruvic  acid  à  lacQc  acid  

à  blood  

2  min  =  maximum  contracQon  

57  

Aerobic  Cellular  RespiraHon  

Makes  ATP  from  glucose  breakdown  in  mitochondria  

If  O2:  Pyruvic  acid  à  mitochondria  à  ATP  

Several  minutes  to  hours  =  maximum  

contracQon  

58  

Muscle  FaHgue  

Feeling  Qred  &  wanQng  to  stop  exercise  =  central  

faHgue  

Low  Ach  &  Ca+2  

Low  creaQne  phosphate  

Low  O2  or  glycogen  

Oxygen  debt  (recovery  oxygen  

uptake)  Build-­‐up  of  lacQc  

acid  

59  

Motor  Units  

One  motor  neuron  +  10-­‐2000  muscle  fibers  (150  fibers  

avg)  

All  fibers  contract  in  unison  

Strength  of  contracQon  depends  on:  the  size  of  a  motor  unit  &  the  #  of  fibers  ac4vated  at  a  give  

4me  

60  

61  

Control  of  Muscle  Tension  

Twitch  contracHon  

Brief  =  20-­‐200  msec  

All  muscle  fibers  in  motor  unit  contract  in  

response  to  AP  

Parts  of  a  Twitch  ContracHon  

Latent  Period  

ContracHon  Period  

RelaxaHon  Period  

Refractory  Period  

62  

63  

64  

Refractory  Period  

65  

Frequency  of  

SHmulaHon  

Wave  summaHon  

Unfused  (Incomplete)  

tetanus  

Fused  (Complete)  tetanus  

Myograms

Forc

e of

con

tract

ion

(a) Single twitch (b) Wave summation (c) Unfused tetanus (d) Fused tetanus Time (msec)

Action potential

67  

Wave  SummaHon  

68  

Unfused  (Incomplete)  

Tetanus  

69  

Fused  (Complete)  

Tetanus  

70  

Why  does  summaHon  &  tetanus  occur?  

Ca+2  remains  in  sarcoplasm  

ElasQc  components  (tendons,  CT)  remain  taut  

Myotonic  goats!  

71  

Motor  Unit  Recruitment  

Large  motor  units  à  High  tension  (Strength)  

Small  motor  units  à  Low  tension  (Precision)  

Motor  units  in  whole  muscle  fire  

asynchronously    Why?  

72  

Muscle  Tone  

Involuntary  contracQon  &  

relaxaQon  of  small  #  of  motor  units  

Alternate  in  constantly  shi\ing  

pa4ern  

No  movement  produced  (but  

muscles  kept  firm)  

FuncQons:  posture,  blood  pressure  

73  

Isotonic  ContracHon  

Generates  movement  

Concentric:  flexion  (muscle  shortens)  

Eccentric:  extension  (muscle  lengthens)  

74  

Isometric  ContracHon  

No  movement  

Maintains  posture  

Maintains  objects  in  fixed  posiQon  

75  

VariaHons  in  Skeletal  

Muscle  Fibers  Differ  in  amount  of  

myoglobin,  mitochondria,  capillaries  

Red  muscle  (darker)  

White  muscle  (lighter)  

Range  of  contracQon  speeds  &  faQgue  

resistance  

76  

3  Types  of  Skeletal  Muscle  Fibers  

Slow  OxidaHve  (SO)  

Fast  OxidaHve  GlycolyHc  (FOG)  

Fast  GlycolyHc  (FG)  

Transverse  secHon  of  three  types  of  skeletal  muscle  fibers  

Slow oxidative fiber

Fast glycolytic fiber

Fast oxidative– glycolytic fiber

LM 440x

78  

Slow  OxidaHve  (SO)  Fibers  

Smallest,  weakest,  slowest  (slow-­‐twitch)  

Red  muscle:  lots  of  mito,  myo,  &  

blood  

Aerobic  cellular  respiraQon  à  ATP  

79  

Slow  OxidaHve  (SO)  

Fibers  

Sustained  contracQons  

High  faQgue  resistance  

Maintains  posture,  yoga  poses  

Aerobic  endurance  acQviQes  (marathon  

running)  

80  

Fast  OxidaHve-­‐GlycolyHc  

(FOG)  Fibers  

Large  diameter  &  strength    

Fast-­‐twitch  

Red  muscle:  lots  of  mito,  myo,  &  blood  

81  

Fast  OxidaHve-­‐GlycolyHc  

(FOG)  Fibers  Aerobic  &  anaerobic  

respiraQon  à  ATP  (store  glycogen)  

Moderate  faQgue  

resistance  

Walking,  sprinQng  

82  

Fast  GlycolyHc  (FG)  Fibers  

Strongest,  fast  twitch  fibers  

High  glycogen  storage  

White  muscle:  less  mito,  myo,  blood  

83  

Fast  GlycolyHc  (FG)  Fibers  

Anaerobic  cellular  

respiraQon  à  ATP  

Low  faQgue  resistance  

Rapid,  intense,  brief  

contracQons:  weight  li\ing  

84  

Cardiac  Muscle  Tissue  

Striated,  branching,  

shorter  fibers  of  heart  

Intercalated  discs  with  gap  juncHons  

One  central  nucleus  per  fiber  

85  

86  

Cardiac  Muscle  Tissue  Same  acQn  &  

myosin  arrangement  as  skeletal  muscle  

Autorhythmic  

Longer  contracQons  (longer  Ca+2  delivery)  

87  

Smooth  Muscle  Tissue  Small,  single,  nonstriated,  tapered,  

involuntary  fibers  

No  T  tubules  &  li4le  SR  

Contains  acQn  &  myosin,  but  no  sarcomeres  

Dense  bodies  

Autonomic neurons

Nucleus

Muscle fibers

(a) Visceral (single-unit) smooth muscle tissue

(b) Multiunit smooth muscle tissue